The present invention relates to a liner for an air flow passage of a gas turbine engine such as the bypass duct of a turbofan gas turbine engine.
The intake and bypass ducts of modern gas turbine engines are lined with acoustic attenuation panels that absorb sound energy and reduce the level of emitted noise. The panels usually work by resonating to the sound energy produced by the engine and dissipating the energy as heat into the air. A conventional acoustic attenuation panel has a perforated sheet which overlays a cellular honeycomb structure.
As well as producing noise, a gas turbine engine generates considerable heat. Cooling systems are needed to keep the components of the engine at operational temperatures. Specialised lubricants and oils are used to cool the components and are usually pumped around the engine in a recirculatory system. The lubricant leaving the hottest parts of the engine must be cooled to prevent overheating and degradation. For this purpose it is known to use a heat exchanger to transfer heat from the lubricant to either the fuel or to air passing through the engine. For example, a surface-air cooled, oil cooler (SACOC) can be mounted on an inner surface of a fan bypass duct. Such a cooler typically has a fin and plate construction with air fins both at inner and outer sides of the cooler and with the oil passing through a central plate in a cross-flow pattern. However, such coolers, while effective at removing heat from the oil, can disturb the flow of air through the duct, which can cause efficiency losses.